Spraying technology is widely used in the anti-corrosion and repair of medium and low pressure boiler tube materials. Among them, the supersonic flame spraying (HVOF coating) has excellent wear resistance and corrosion resistance, and the anti-corrosion and repair thermal spraying technology of medium and low pressure boiler tube materials is an important and mature surface treatment technology. It has become a thermal spraying technology. The mainstream development direction is also widely used in metallurgy, machinery manufacturing, petrochemical, electric power and other industrial fields.
Different values of the chemical composition will result in different material characteristics. When the chemical composition has a large range, the performance difference will fluctuate in a large range, so that the comprehensive performance of the profile cannot be controlled. Therefore, optimizing the chemical composition of medium and low pressure boiler tubes becomes the most important part of the production of high-quality aluminum alloy building profiles. The role of alloying elements and their effects on performance The medium and low pressure seamless boiler tube is a medium-strength heat-treatable and strengthened alloy in the AL-Mg-Si series. The main alloy elements of Mg and Si in the medium and low pressure boiler tube are determined. Mg and Si percentage content 6063 control range 2.1Mg control range Mg is flammable medium and low pressure boiler tube, there will be burnt during the smelting operation. When determining the Mg control range, the error caused by burning should be considered, but it should not be too wide to prevent the alloy performance from getting out of control. According to experience and the level of our factory's ingredients, smelting and laboratory tests, the Mg fluctuation range is controlled within 0.04%, and the T5 profile is 0.47% 0.50%, and the T6 profile is 0.57% 0.60% 3. Si control range for medium and low pressure boiler tubes When the Mg range is determined, the Si control range can be determined by the Mg/Si ratio. Because the factory controls Si to be 0.09% 0.13%, Mg/Si should be controlled between 1.181.32.
The selection range of the chemical composition of the T5 and T6 state profiles of the medium and low pressure boiler tubes. If you want to change the alloy composition, for example, if you want to increase the amount of Mg2Si to 0.95% to facilitate the production of T6 profiles, you can move Mg up to about 0.6% along the upper and lower limits of Si. At this time, Si is about 0.46% Si and 0.11% Mg/Si is 1. 4According to our factory's experience, the amount of Mg2Si in the middle and low pressure boiler tube profiles is controlled within the range of 0.75% and 0.80%, which can fully meet the requirements of mechanical properties. The normal extrusion coefficient (when it is greater than or equal to 30, the tensile strength of the profile is within the range of 200240MPa. This control of the alloy not only has good plasticity, easy extrusion, high corrosion resistance and good surface treatment performance, but also can Save alloying elements. However, special attention should be paid to strictly controlling the impurity Fe. If the Fe content is too high, the extrusion force of the 20g high-pressure boiler tube will increase, the surface quality of the extruded material will deteriorate, the anodic oxidation color difference will increase, and the color will be gray. While dull, Fe also reduces the plasticity and corrosion resistance of the alloy. Practice has proved that it is ideal to control the Fe content within the range of 0.15% and 0.25% with styrene-acrylic emulsion, molybdate, phytic acid, and organic A chromium-free passivation film was prepared with silane as the main raw material. The aluminum tube adopts lead acetate drop accelerated corrosion test (ASS neutral salt spray corrosion test (NSS). The composition of the passivation solution, reaction temperature, stirring time, etc. According to the influence of corrosion, the optimal preparation conditions are: 300mLL^-1 styrene-acrylic emulsion, 12mLL^-1 phytic acid solution, 80mLL^-1 organosilane, 60mLL^-1 composite salt solution, reaction temperature is 30℃, The chromium-free passivation film prepared by stirring for 3 hours has stable performance and excellent corrosion resistance.